Dioxopromethazine began to be used in therapy as a modern antihistamine agent in the 1970s. A dioxopromethazine-containing ophthalmic instillation and a gel were employed until the end of the 1990s. The paper deals with the examination of the stability of the drug dioxopromethazine in aqueous solutions and the ophthalmic instillation Promefrin® stored under different conditions. High-performance liquid chromatography with spectrophotometrical and electrochemical detection and HPLC connected on-line with mass spectrometry were employed for analysis. Dioxopromethazine in aqueous solutions and in ophthalmic instillations stored in direct sunlight was found not to be stable. However, the cover of the ophthalmic instillation, a brown-glass prescription bottle, and observation of storing conditions sufficiently protect the active ingredient from decomposition processes.

        Key words: dioxopromethazine – Promefrin® – stability – HPLC